Just trying to get a handle on stepping up a yeast starter. I have 11 gal. of IPA with a OG of 1.066, I believe I will need approx. 500 billion cells. So Roughly 6.67 liter starter. What do I start with and how do I get it to grow enough cells?

How did you come up with 6.67 liters of starter? That's almost a gallon and a half, which is an awful lot for an 11 gallon batch; about 10% of the brew length. Obviously the amount of liquid will depend on the concentration of yeast cells.

When propping up a batch of yeast, you typically want to go in steps of X10.